keycloak, why does backend channels need a redirect url

Question

I try to integrate my Python app(backend client) into the Keycloak system using openid connect, why do I have to fill the Valid Redirect URIs field? From my understanding for OAuth 2.0, the backend channel just need to exchange the code for id and access tokens in the Authorization Code Flow process

Why do we need a redirect URL here, shouldn't it only filled in the front end client?

Any Ideas?

Answer 1

The client which receives the authorization code and the one which exchanges the code for tokens must be the same client - at least from the Authorization Server's point of view. Theoretically you can have separate applications which handle parts of the OAuth flow, but they must be using the same client ID.

Ideally, the redirect URI points to an endpoint exposed by your Python backend. After Keycloak (or any Authorization Server) finishes authentication and authorization, it will redirect the user to that endpoint together with the authorization code. This way the authorization code will go straight to the backend client, the frontend app will never have to handle it. By registering the URL you want to make sure that no one performs authorization using your client ID, but asks to send the code to another application.